H2s conversion to sulfur using a regenerated iodine solution

ABSTRACT

Systems and methods of removing sulfur from a gas stream comprising hydrogen sulfide (H 2 S) is provided. The systems and methods may utilize iodine to remove sulfur from the gas stream. In certain systems and methods, the iodine may be regenerated. In particular, the present systems and methods may be capable of reducing sulfur content in a gas stream comprising hydrogen sulfide H 2 S gas to levels that are undetectable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/398,918filed Feb. 17, 2012, which claims the benefit of U.S. ProvisionalApplication No. 61/444,383 filed Feb. 18, 2011, each of which areincorporated by reference in its entirety for all purposes.

FIELD OF THE DISCLOSURE

The present invention generally relates to systems and methods ofremoving sulfur from a gas stream comprising hydrogen sulfide (H₂S)using an iodine solution. In certain systems and methods, the iodinesolution is regenerated. In particular, the present systems and methodsare capable of reducing sulfur content in a gas stream comprisinghydrogen sulfide H₂S gas to levels that are undetectable.

SUMMARY OF THE DISCLOSURE

In accordance with one or more embodiments, the invention relates to amethod for treating hydrogen sulfide gas. The method may comprisereacting hydrogen sulfide gas with iodine to produce a stream comprisingiodide and sulfur, removing sulfur from the stream to produce aseparated stream comprising iodide, and reacting the separated streamcomprising iodide with a source of oxygen under aqueous conditions andat a predetermined temperature and a predetermined pressure to produce astream comprising iodine.

In certain embodiments, the method may further comprise recovering atleast a portion of the iodine from the stream comprising iodine. In atleast one embodiment, the method may further comprise introducing atleast a portion of the regenerated iodine to the hydrogen sulfide gas.

In certain embodiments, the method further comprises recoveringelemental sulfur from the stream comprising iodide and sulfur. Incertain aspects, the method may use air as the source of oxygen. Inanother aspect, the method may use a predetermined temperature in arange of from about 75° C. to about 260° C. In at least one embodiment,the method may use a predetermined temperature in a range of from about120° C. to about 175° C.

In at least one aspect, the method may use a predetermined pressure in arange of from about 25 psi to about 2000 psi. In yet another aspect, themethod may use a predetermined pressure in a range of from about 100 psito about 400 psi. In certain aspects, the method may further comprisereacting the separated stream comprising iodide with a source of oxygenunder aqueous conditions for a time period in a range of from about 15minutes to about 120 minutes. In at least one aspect, the method mayfurther comprise reacting the separated stream comprising iodide with asource of oxygen under aqueous conditions for a time period of less thanabout 15 minutes.

In another aspect, the method further comprises recovering thermalenergy from the stream comprising iodine.

In accordance with one or more embodiments, the invention relates to asystem for treating hydrogen sulfide gas. The system may comprise acontactor fluidly connected to a source of hydrogen sulfide gas and asource of iodine, a separator fluidly connected downstream from thecontactor and configured to separate elemental sulfur and iodide, and areactor fluidly connected downstream from the separator and theseparated iodide and fluidly connected to a source of oxygen.

In certain embodiments, the system may further comprise a control systemconfigured to regulate a predetermined temperature and predeterminedpressure of the reactor. In certain aspects, the system may furthercomprise at least one scrubber that may be fluidly connected downstreamfrom the reactor and upstream from the source of iodine. In anotheraspect, the system may further comprise at least one energy recoverydevice fluidly connected downstream from the reactor and upstream fromthe contactor and configured to recover thermal energy from the reactor.In certain aspects, the system may further comprise a reactor outletfluidly connected upstream from the contactor and configured to transferat least a portion of regenerated iodine from the reactor to thecontactor. In at least one embodiment, the system may have a rate ofregeneration from iodide to regenerated iodine from the reactor of atleast 50%. In certain embodiments, the system further comprises ascrubber fluidly connected downstream from the reactor and configured totransfer at least a portion of regenerated iodine from the reactor tothe contactor.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a schematic drawing of a process flow diagram in accordancewith one or more aspects of the disclosure;

FIG. 2 is a schematic drawing of a process flow diagram in accordancewith one or more aspects of the disclosure;

FIG. 3 is a schematic drawing of a process flow diagram in accordancewith one or more aspects of the disclosure;

FIG. 4 is a schematic drawing of a process flow diagram in accordancewith one or more aspects of the disclosure;

FIG. 5 is a schematic drawing of a process flow diagram in accordancewith one or more aspects of the disclosure; and

FIG. 6 is a schematic drawing of a process flow diagram in accordancewith one or more aspects of the disclosure.

DETAILED DESCRIPTION

The systems and methods described herein are not limited in theirapplication to the details of construction and the arrangement ofcomponents set forth in the description or illustrated in the drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting. The use of “including,” “comprising,” “having,”“containing,” “involving,” “having,” “containing,” “characterized by,”“characterized in that,” and variations thereof herein is meant toencompass the items listed thereafter, equivalents thereof, as well asalternate embodiments consisting of the items listed thereafterexclusively. Use of ordinal terms such as “first,” “second,” “third,”and the like in the claims to modify a claim element does not by itselfconnote any priority,

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (forexample, it includes at least the degree of error associated with themeasurement of the particular quantity). When used in the context of arange, the modifier “about” should also be considered as disclosing therange defined by the absolute values of the two endpoints. For example,the range “from about 2 to about 4” also discloses the range “from 2 to4.”

As used herein, the terms “iodine species,” “iodine solution,” and“iodine-rich solution,” can refer to iodine in at least one of itsvarious forms, including diatomic iodine or elemental iodine (I₂),iodide (I⁻), triiodide (I₃ ⁻), and iodate (IO₃ ⁻).

As used herein, the terms “iodine,” “elemental iodine,” “moleculariodine,” or “free iodine” refers to the diatomic molecule I₂.

As used herein, the term “iodide,” “iodide ion,” or “iodide anion”refers to the species that is represented by the chemical symbol I⁻.Suitable counter-ions for the iodide anion include sodium, potassium,calcium and the like.

Elemental iodine is soluble in most organic solvents, but is onlyslightly soluble in water. The solubility increases by the presence ofthe iodide ion. Molecular iodine reacts reversibly with the negativeion, generating triiodide anion I₃ ⁻ in equilibrium, which is soluble inwater. The reaction for formation of the iodide complex is as follows:

I₂+I⁻⇄I₃ ⁻

As used herein, the terms “I₃ ⁻,” “I₃ ⁻ complex,” or “triiodide” referto the ion formed from the reversible reaction between I₂ and I⁻.

As used herein, the term “iodate” or “iodate anion,” refers to thespecies that is represented by the chemical formula IO₃ ⁻. Suitablecounter-ions for the iodate anion include sodium, potassium, calcium andthe like.

As used herein, the term “acid gas” refers to a gas mixture whichcontains significant amounts of H₂S, carbon dioxide (CO₂), or similarcontaminants.

As used herein, the terms “separator” or “clarifier” refer to anysuitable apparatus for performing a separation process on a multi-phasefluid into separate phases. For example, a separator may comprise adevice that separates a two-phase liquid/solid fluid into separateliquid and solid phases. Separators may separate fluids or solids, orfluids from solids.

As used herein, the term “oxidation” refers to a reaction in which theatoms in an element lose electrons and the valence of the element iscorrespondingly increased.

H₂S is a common byproduct of processing natural gas and refininghigh-sulfur crude oils. This may be largely due to the fact that sulfurmust be removed from fuels in order to meet environmental regulationsand minimize corrosion in an internal combustion engine due to sulfuroxide (SO_(x)) production. The term SO_(x) as used herein refers to thespecies SO₂ and SO₃. The most common method of handling the H₂S streamis to produce elemental sulfur via the Claus process. The basic Clausunit comprises a thermal stage and two or more catalytic stages. Some ofthe H₂S in the feed gas is thermally converted to SO₂ in the reactionfurnace of the thermal stage according to reaction (2) below. Theremaining H₂S is then reacted with the thermally produced SO₂ to formelemental sulfur in the thermal stage and the subsequent catalyticstages according to reaction (1) below. The catalyst is typicallyalumina, although other catalysts may be used.

The basic chemical reactions occurring in a Claus process arerepresented by the following reactions:

2H₂S+SO₂→3S+2H₂O  (1)

To provide the proper ratio of components, the first step in the Clausprocess is the combustion of ⅓ of the H₂S in the feed gas:

H₂S+1.5O₂→SO₂+H₂O  (2)

Combining equations (1) and (2), the overall process reaction is:

2H₂S+O₂→2S+2H₂O  (3)

The Claus process is estimated to only be about 95-98% efficient atsulfur removal. The Claus plant tail gas is routed either to a tail gastreatment unit for further processing, or to a thermal oxidizer(incinerator) to incinerate all of the sulfur compounds in the tail gasto SO₂ before dispersing the effluent to the atmosphere. Theincineration process is a very energy intensive step and causes therelease of a significant amount of SO_(x) to the environment.

A Claus system at a petrochemical refinery can produce more than 500tons of sulfur per day. Since the process is only about 95-98%efficient, about 2-5%, or about 10-30 tons per day of SO₂, a majorsource of acid rain, is released to the environment. Regulations incertain jurisdictions require minimum sulfur removal levels of98.8-99.8% or above, which requires the installation of a tail gastreatment unit downstream of the Claus plant and upstream of theincinerator.

Wet Air Oxidation (WAO) is a technology that has been adopted in thetreatment of process streams, and is widely used, for example, to removepollutants in wastewater. In certain applications, WAO can be used torecover and regenerate chemicals for re-use. The method of wet oxidationinvolves the aqueous phase oxidation of a target constituent by anoxidizing agent, for example, molecular oxygen from an oxygen-containinggas such as air, at elevated temperatures and pressures.

As used herein, the terms “wet air oxidation” (WAO) and “wet oxidation”(WO) are used interchangeably, and in general refer to the oxidation ofsoluble or suspended components in an aqueous environment using oxygenas the oxidizing agent. When air is used as the source of oxygen, theprocess is often referred to as wet air oxidation. When pure oxygen isthe source of oxygen, the process is often referred to as wet oxidation.

Iodine is a mild oxidant that is capable of converting H₂S to sulfur.The reaction of H₂S with iodine to form elemental sulfur and iodic acid(HI) may be used as a method to prepare HI. WAO may then be used tooxidize the iodide to iodine. The resulting system produces elementalsulfur and regenerated iodine. The chemistry of the two reactions is:

H₂S+I₂→S+2HI  (I)

2HI+1/2O₂→I₂+H₂O  (II)

The sulfur generation reaction (reaction I) may be completed, forexample, by introducing H₂S gas or a gas stream comprising H₂S to acontactor or scrubber containing an iodine-rich solution. The I₂ reactswith H₂S, producing a solution comprising elemental sulfur, iodic acid,and possibly, other iodide salts, such as potassium iodide (KI) and(NaI).

The iodine regeneration reaction (reaction II) may be completed, forexample, by using WAO reaction techniques, where an oxygen-rich gas maybe introduced to a reactor under predetermined temperatures andpredetermined pressures to convert the iodide to iodine.

Reactions (I) and (II) are exothermic, which may allow for opportunitiesto recover energy in the form of heat.

In accordance with one or more embodiments, the invention relates to oneor more systems and methods of treating hydrogen sulfide gas. In certainembodiments, the system may receive one or more feed streams comprisingH₂S. In certain aspects, the system may receive one or more H₂S feedstreams from industrial sources. For example, the H₂S feed stream mayoriginate from a chemical processing facility or oil refinery. As usedherein, the term “H₂S feed stream” refers to any composition thatcomprises H₂S, such as, for example, acid gas and sour gas.

In certain embodiments, the H₂S feed stream may be in the form of acidgas. In certain aspects, acid gas has a composition that is in a rangeof from about 60 to about 70% H₂S and from about 30 to about 40% CO₂. Inother aspects, acid gas has a composition of about 67% H₂S and about 33%CO₂. In certain embodiments, acid gas has a composition of about 66% H₂Sand about 34% CO₂. In other non-limiting embodiments, the acid gas has acomposition of about 60% H₂S and about 40% CO₂.

In certain embodiments, the H₂S feed stream may be in the form of sourgas. As used herein, the term “sour gas” refers to natural gas thatcomprises H₂S.

In certain exemplary embodiments, the H₂S feed stream may furthercomprise water. In certain non-limiting embodiments, the H₂S feed streammay be pre-treated before being introduced to the process system. Forexample, the H₂S feed stream may be pre-heated. A source of H₂S feedstream may take the form of direct piping from at least one of a plant,process, or holding vessel.

In one or more embodiments, hydrogen sulfide gas may be reacted withiodine. In certain non-limiting embodiments, the system may receive atleast a portion of iodine in the form of regenerated iodine from a wetoxidation process. In certain embodiments, the system may receive atleast a portion of iodine in the form of iodine species, for example,the I₃ ⁻ complex. In certain embodiments, the system may receive atleast a portion of iodine in the form of iodine solution comprisingiodine (I₂) and iodide (I⁻). In various embodiments, the system mayreceive at least a portion of iodine in the form of iodine solutioncomprising iodine (I₂), iodide (I⁻), and triiodide (I₃ ⁻). In certainaspects, the source of iodide may be HI. In certain embodiments, thesystem may receive at least a portion of iodine in the form ofregenerated iodine from a scrubbing process. In certain embodiments, atleast a portion of the iodine solution may be pre-treated before beingintroduced to the process system. For example, the iodine solution maybe pre-heated or filtered. A source of iodine or iodine solution to beintroduced to the system may take the form of direct piping from aplant, process, or holding vessel. In certain embodiments, the source ofiodine or iodine solution may be from a holding vessel that may beblanketed with nitrogen gas.

Although the description exemplifies the use of iodine to react with H₂Sand produce sulfur, it is within the scope of the methods and systemsdescribed here to use other suitable compounds that are capable offunctioning as oxidizers and being regenerated, for example, by a wetoxidation process. Non-limiting examples of other compounds that may besuitable to use include, but are not limited to, chlorine, bromine,manganese, vanadium, and fluorine.

In accordance with one or more embodiments, hydrogen sulfide gas may bereacted with iodine in a contactor. As used herein, the terms“contactor” or “impinger” refer to any suitable apparatus in which twophases can be brought into contact with one another in either co-currentor countercurrent flow for purposes of conducting a reaction. The devicemay be constructed as a column that may further comprise suitablecomponents, for example, at least one of baffles and packing, to improveat least one of mass transfer, heat exchange, and reaction kinetics. Asused herein, the term “baffle” may refer to a device that regulates theflow of a fluid. In certain embodiments, the contactor may beconstructed and arranged to allow separation of gas and liquid phases.In certain aspects, the residence time for at least one gas in thecontactor is from about 1 to about 10 minutes. In at least one aspect,the residence time for a liquid in the contactor is from about 1 toabout 120 minutes. In a different aspect, the residence time for aliquid in the contactor is from about 1 to about 10 minutes. In certainembodiments, the contactor may be fluidly connected to a source ofsteam.

In certain embodiments, the hydrogen sulfide gas may be reacted withiodine at a temperature and pressure sufficient for the hydrogen sulfideto be converted to elemental sulfur. For example, the hydrogen sulfidegas may be reacted with iodine at a temperature that is sufficient tokeep sulfur in the liquid phase. In addition, the hydrogen sulfide gasmay be reacted with iodine at a temperature that is above the meltingpoint of sulfur and iodine but below the temperature at which sulfurbecomes viscous. In certain embodiments, the temperature may be in arange of from about 15° C. to about 260° C. In certain otherembodiments, the temperature may be in a range of from about 120° C. toabout 175° C. In certain embodiments, the hydrogen sulfide gas may bereacted with iodine at a pressure in a range of from about 25 psi toabout 2000 psi. In certain embodiments, the hydrogen sulfide gas may bereacted with iodine at a pressure in a range of from about 100 psi toabout 400 psi.

In accordance with one or more embodiments, the percent sulfur removedfrom the H₂S feed stream may be in a range of from about 90% to about100%. In certain embodiments, the percent sulfur removed from the H₂Sfeed stream may be in a range of from about 95% to about 100%. Incertain embodiments, the percent sulfur removed from the H₂S feed streammay be in a range of from about 97% to about 100%. In certainembodiments, the percent sulfur removed from the H₂S feed stream may beat least about 99%.

In certain embodiments, the reaction between hydrogen sulfide gas andiodine produces a stream comprising one or more phases or components.The reaction may comprise a first phase that may be a gas or an off-gas.In at least one embodiment, the first phase may be transferred from thecontactor. In one or more aspects, the first phase may comprise watervapor. In certain embodiments, the first phase comprising water vapormay be transferred to a condensor. In certain embodiments, the condensormay condense the transferred water vapor into liquid water. In certainother embodiments, the first phase may comprise iodine. In variousembodiments, the first phase may comprise iodine solution comprisingiodine (I₂), iodide (I⁻), and triiodide (I₃ ⁻). In at least oneembodiment, the first phase comprising iodine or iodine solution may betransferred to a scrubber. In certain embodiments, iodine may beregenerated from the first phase comprising iodine or iodine solution bytreating it with a scrubber. In other embodiments, the regeneratediodine from the first phase and treated by the scrubber may bere-introduced to the process system as a source of regenerated iodine.In certain embodiments, the first phase may comprise CO₂. In certainembodiments, the first phase comprising CO₂ may be transferred to acooler. In at least one aspect, the first phase may comprise smallconcentrations of impurities contained in the original H₂S feed stream.

In at least one embodiment, the reaction between hydrogen sulfide gasand iodine may produce a stream comprising a second phase. In certainaspects, the second phase may be a fluid comprising a liquid and asolid. In certain embodiments, the hydrogen sulfide gas may be reactedwith iodine to produce a stream comprising iodide and sulfur. In certainaspects, the hydrogen sulfide gas may be reacted with iodine to producea stream comprising iodide, sulfur, and sulfuric acid. In one or moreaspects, the stream may comprise iodide in the liquid phase and sulfurin the solid phase. In certain aspects, the stream may comprise at leastone of sulfur, sulfuric acid, iodine, iodic acid, and iodide salts. Incertain other aspects, the stream may comprise sulfur in the solid phaseand at least one of iodine, iodic acid, and iodide salts in the liquidphase.

In accordance with one or more embodiments, the method for treatinghydrogen sulfide gas may further comprise removing sulfur from thestream comprising iodide and sulfur. In certain aspects, the sulfur maybe separated from the stream using a separator. In certain embodiments,the separator may be connected downstream from the contactor. In certainaspects, the separator may separate two liquid phases. In other aspects,the separator may separate a solid from a liquid phase. In at least oneaspect, the separator may separate sulfur in the solid phase from iodidein the liquid phase. In certain aspects, the recovered sulfur may bepure enough to be a viable commercial product that may be furtherprocessed onsite or offsite and sold.

In at least one aspect, the method for treating hydrogen sulfide gas mayfurther comprise recovering or removing water from the contactor. Therecovered water may be recovered in the gas or liquid phase. Therecovered water be recovered in the gas phase and further condensed tothe liquid phase. The recovered water may be sold or used for furtherprocess treatments.

In accordance with one or more embodiments, the method for treatinghydrogen sulfide gas may further comprise removing sulfur from thestream comprising iodide and sulfur to produce a separated streamcomprising iodide. In at least one aspect, the separated stream maycomprise iodine, iodic acid, and iodide salts. In various embodiments,the separated stream may comprise iodine species, iodic acid, and iodidesalts. In certain aspects, the separator may be configured to separateelemental sulfur and iodide. In other aspects, the method may furthercomprise recovering elemental sulfur from the stream comprising sulfurand iodide. In at least one aspect, the solution may contain at leastabout 67% of the total I⁻ as HI. In certain embodiments, the separatedstream may comprise less than about 10 mg/L of sulfur.

As previously mentioned, reactions (I) and (II) are exothermic, whichmay allow for opportunities to recover thermal energy in the form ofheat. Some aspects of the methods and systems disclosed herein mayinvolve transferring at least a portion of heat from one or more streamscoming from one or more process components to one or more streams goingto one or more other process components. For example, one or moreembodiments may include at least one energy recovery device in fluidcommunication with the reactor for the purposes of capturing thermalenergy from the wet oxidation reaction. In addition, one or moreembodiments may include at least one energy recovery device in fluidcommunication with at least one of the contactor and separator for thepurposes of capturing thermal energy from the reaction between hydrogensulfide and iodine. One or more embodiments may include at least oneenergy recovery device in fluid connection between a stream coming fromthe reactor and going to the contactor. In at least one aspect, thermalenergy may be recovered from the stream comprising iodide. In certainembodiments, energy may be recovered from one or more reactions,streams, or components of the process to be used in another related orunrelated to the processes disclosed herein.

In accordance with one or more embodiments, the method for treatinghydrogen sulfide gas may further comprise reacting the separated streamcomprising iodide in a wet oxidation process. The separated streamcomprising iodide may be oxidized with an oxidizing agent. The oxidizingagent may be oxygen-containing gas, for example, air, oxygen-enrichedair, or pure oxygen. As used herein, the phrase “oxygen-enriched air” isdefined as air having oxygen content greater than about 21%. In certainembodiments, the separated stream comprising iodide may be oxidized witha source of oxygen under aqueous conditions. In at least one embodiment,the separated stream comprising iodide may be pre-heated.

In certain embodiments, the separated stream comprising iodide may bereacted with a source of oxygen under aqueous conditions in a reactor.As used herein, the term “reactor” may refer to any suitable device inwhich a chemical reaction occurs. In certain aspects the reactor may befluidly connected downstream from the separator and the separatediodide. In at least some aspects, the reactor may be fluidly connectedto a source of oxygen. In at least one aspect, the source of oxygen maybe supplied to the reactor in pressurized form. The reactor may beconfigured for batch or continuous flow processes. The reactor may beconstructed as a column that may further comprise suitable components,for example, at least one of baffles and packing, to improve at leastone of mass transfer, heat exchange, and reaction kinetics. In certainembodiments, the reactor may be constructed and arranged to allowseparation of gas and liquid phases. In certain non-limitingembodiments, the reactor may be fluidly connected to a source of steam.In other embodiments, the reactor may be fluidly connected to a sourceof air. In certain embodiments, the reactor may be fluidly connected toa source of pure oxygen.

In certain embodiments, the iodide may be reacted with a source ofoxygen under aqueous conditions and a predetermined temperature and apredetermined pressure to allow for the conversion of iodide to iodine.In certain embodiments, the predetermined temperature may be in a rangeof from about 75° C. to about 260° C. In certain aspects, thepredetermined temperature may be in a range of from about 120° C. toabout 175° C. In certain embodiments, the predetermined pressure may bein a range of from about 25 psi to about 2000 psi. In certainembodiments, the predetermined pressure may be in a range of from about100 psi to about 400 psi. In at least one aspect, the separated streamcomprising iodide may be reacted with a source of oxygen under aqueousconditions for a time period in a range of from about 15 minutes toabout 120 minutes. In certain embodiments, the separated streamcomprising iodide may be reacted with a source of oxygen under aqueousconditions for a time period to allow for the conversion of iodide toiodine. In certain embodiments, the time period may be in a range offrom about 15 minutes to about 30 minutes. In at least one aspect, theseparated stream comprising iodide may be reacted with a source ofoxygen under aqueous conditions for a time period of less than about 15minutes.

In accordance with one or more embodiments, the separated streamcomprising iodide may be reacted with a source of oxygen under aqueousconditions and at a predetermined temperature and a predeterminedpressure to produce a stream comprising iodine. In certain non-limitingembodiments, at least a portion of the iodine from the stream comprisingiodine may be regenerated. In at least one aspect, the stream comprisingiodine comprises iodine species. In certain aspects, at least a portionof the regenerated portion of the iodine from the stream comprisingiodine may be introduced to the hydrogen sulfide gas. In at least oneembodiment, a reactor outlet may be fluidly connected upstream from thecontactor. In certain embodiments, the reactor outlet may be configuredto transfer at least a portion of regenerated iodine from the reactor tothe contactor. In certain aspects, at least a portion of the regeneratedportion of the iodine from the stream comprising iodine may beintroduced to the process system as a source of regenerated iodine.

In at least one embodiment, the rate of regeneration from iodide toregenerated iodine from the reactor is at least 50%. This level ofregeneration is considered surprising and unexpected, since oxidationreactions are typically considered to be destructive techniques, capableof destroying one or more chemical bonds in liquid and gas phases.Accordingly, the systems and methods of the present disclosure providefor cost savings, related to the unexpected ability to regenerate andre-use iodine in the process.

In contrast to a wet oxidation process, the Fenton reaction is acatalytic method based on the generation of highly reactive hydroxylradicals from hydrogen peroxide in the presence of a metallic ion,commonly Fe(II), or other low valence transition metals, Fe(III), Cu(II)or Mn(II) dissolved in an aqueous medium. In general, the Fentonreaction utilizes a solution of aqueous hydrogen peroxide and an ironcatalyst to oxidize contaminants or waste waters. Ferrous iron (II) isfirst oxidized by hydrogen peroxide to ferric iron (III), a hydroxylradical and a hydroxyl anion. Iron (III) is then reduced back to iron(II), a peroxide radical, and a proton by the same hydrogen peroxide.The reaction chemistry is as follows:

Fe²⁺+H₂O₂→Fe³⁺+OH.+OH⁻  (1)

Fe³⁺+H₂O₂→Fe²⁺+OOH.+H⁺  (2)

In practice, the iron activates the hydrogen peroxide, creating hydroxylradicals which are capable of oxidizing organic material found inwastewater. The Fenton process is generally efficient under acidicconditions and atmospheric pressure. In contrast, wet air oxidationreactions typically take place under elevated temperatures andpressures, where the high temperatures enhance reaction kinetics and thehigh pressures increase the oxidant (air or oxygen) solubility in theaqueous reaction medium. In addition, wet air oxidation involves takingoxygen from the gas phase to the liquid phase to act as a reactant.

In certain embodiments, the reaction between iodide and the source ofoxygen may produce an off-gas. In at least one embodiment, the off-gasmay be transferred from the reactor. In one or more aspects, the off-gasmay comprise at least one of nitrogen, oxygen, iodine, and water. Inanother aspect, the off-gas may comprise at least one of nitrogen,oxygen, iodine species, and water. In at least one aspect, water may berecovered from the off-gas by transferring it to a scrubber. In at leastone embodiment, the off-gas comprising iodine may be transferred to ascrubber. In certain aspects, iodine may be regenerated from the off-gasby treating it with a scrubber. In another aspect, the regeneratediodine from the scrubber may be re-introduced to the process system as asource of regenerated iodine. In at least one aspect, the scrubber maybe fluidly connected downstream from the reactor and upstream from thesource of iodine. In at least one embodiment, at least one energyrecovery device may be fluidly connected downstream from the reactor andmay be configured to recover thermal energy from the reactor. In certainembodiments, the energy recovery device may be a heat exchanger.

In accordance with certain embodiments, the system for treating hydrogensulfide gas may further comprise a control system. In certainembodiments, the control system may monitor and regulate operation ofone or more parameters of any unit operation or stream of the processsystem. In certain aspects, the control system may be utilized toperform at least one of monitoring, regulating, and adjusting operatingconditions of any of the unit operations or streams of the processsystem based on targeted or predetermined values. The targeted orpredetermined values may be selected to achieve at least one of aselected or desired product or product quality, a selected or desirableefficiency of the process system, and a selected or desired recoveryrate of the one or more components, reactants, or products of thesystem. For example, the control system may be configured to regulate apredetermined temperature. In other examples, the control system may beconfigured to regulate a predetermined pressure. In some embodiments,the same or a different control system can be utilized to perform atleast one of monitoring, adjusting, and regulating operating conditionsin any of the unit operations of the system. For example, the flow rateof the H₂S feed stream may be monitored and controlled to provide one ormore predetermined, target, or set point values, or to be dependent onother operating conditions of one or more other unit operations. Othermonitored or controlled parameters can be the temperature, the pressure,and the flow rates of any of the streams. The controller may beimplemented using one or more computer systems, which may be, forexample, a general-purpose computer or a specialized computer system.

One or more embodiments of the systems and methods described here mayinclude one or more fluid control devices, such as pumps, valves,regulators, sensors, pipes, connectors, controllers, power sources, andany combination thereof.

FIG. 1 illustrates a process flow diagram in accordance with the methodsand systems described here. The process system 10 includes contactor 101where H₂S feed stream 100, and iodine, which may be in the form ofiodine-rich solution, 106 are introduced and mixed together. The iodinereacts with H₂S to produce stream 104. Stream 104 may comprise at leastone of elemental sulfur, iodide in the form of HI, un-reacted I₂, andother iodide salts. Stream 104 may then be introduced into separationdevice or separator 102, where elemental sulfur 120 may be precipitatedoff and the remaining iodide in the form of iodide solution 105, may betransferred to reactor 103, where a wet oxidation reaction occurs.Iodide solution 105 may comprise HI and other iodide salts. In certainnon-limiting embodiments, iodide solution 105 may be pre-treated beforebeing introduced to reactor 103. For example, iodide solution 105 may bepre-heated or filtered. For instance, iodide solution 105 may be heatedto a temperature that is sufficient to create the desired reactionconditions to convert iodide to iodine. A source of oxygen, such as airor pure O₂ may be introduced to reactor 103 under aqueous conditions,for example, by introducing steam. Under conditions of high temperatureand pressure, the iodide may be oxidized to iodine. The regeneratediodine-rich solution 106 may be removed from the system or may berecycled back to contactor 101. Gas effluent 122 off of the contactormay comprise CO₂ and off-gas from the wet oxidation reaction.

A process flow diagram in accordance with one or more embodiments of themethods and systems described herein is shown in FIG. 2. The processsystem 20 includes a contactor 201, where H₂S feed stream 200 may beintroduced and mixed with iodine, which may be in the form ofiodine-rich solution, 206. H₂S feed stream 200 may originate from one ormore chemical processing facilities or oil refineries located upstreamor downstream from process system 20. The H₂S may be mixed with andreact with I₂ in the contactor to produce stream 204, which exitscontactor 201, and may comprise at least one of elemental sulfur,un-reacted I₂, iodide in the form of HI, and other iodide salts. Off-gas222 from contactor 201 may contain at least one of un-reacted CO₂,iodine species, and small concentrations of impurities from original H₂Sfeed stream 200. Off-gas 222 may be additionally treated to regenerateat least one of I₂ and CO₂. A cooler, for example, a tube-in-pipecooler, may treat CO₂ contained in off-gas 222 Other suitable types ofcoolers may include, for example, air coolers, shell and tube coolers,thin fin, and plate and frame coolers.

Stream 204 may then be passed through separation device or separator202, where elemental sulfur 220 may be precipitated off. The separationdevice may also separate two phases as liquids. The remaining portionfrom contactor 201 may produce stream 212, which may comprise HI andother iodide salts. A first portion of stream 212 may produce iodidesolution stream 205, which may be introduced into reactor 203, where awet oxidation reaction occurs. Air 224 and steam 226 may be introducedto reactor 203 to produce regenerated I₂, which may exit reactor 203 asstream 211. Regenerated iodine stream 211 may be used to comprise aportion of iodine feed stream 206. Off-gas 228, exiting from reactor203, may contain at least one of nitrogen, un-reacted O₂, water producedby the reaction, and un-reacted I₂. Scrubber 207 may be used toregenerate additional I₂, in the form of regenerated iodine stream 210,which may exit scrubber 207 and may be further used to comprise aportion of iodine feed stream 206. Water 230 recovered or produced bythe scrubber may exit through one or more scrubber outlets. Scrubber 207may produce off-gas 228, comprising at least one of nitrogen, unreactedoxygen, and noncondensable gases. A second portion of iodide solutionstream 212 may produce iodide solution 209, which may be transferred toscrubber 207 and may serve to aid in I₂ regeneration.

Additional processing or flow regulating equipment may also be placedthroughout the process flow system. For example, a pump may be placed incommunication with iodide solution 212. In addition, a valve device maybe placed in fluid communication with iodide solution 212 to produce theappropriate proportional separation between iodide solutions 205 and209.

The iodine regeneration reaction II is exothermic and the temperature ofreactor 203 may be slightly higher than contactor 201. These conditionsmay provide an opportunity to recover energy from reactor 203, in theform of heat, using energy recovery device 208. Energy recovery device208 may be positioned, for example, in fluid communication withregenerated iodine feed stream 211, exiting from reactor 203, and atleast one of regenerated iodine feed stream 210, exiting from thescrubber, and iodine feed stream 206. A suitable example of energyrecovery device 208, may be, but is not limited to, one or more heatexchangers.

Suitable construction materials for the process equipment, such as thecontactors, separators, reactors, energy recovery devices, and pipes,include materials that are corrosion resistant and able to withstandhigh temperatures and pressures. Non-limiting examples of suitablematerials include, but are not limited to, tantalum, titanium, includingtitanium grade 2, and Alloy C-276 (a nickel alloy plate available, forexample, from Sandmeyer Steel Company, Philadelphia, Pa.). In addition,Teflon®-lined and glass-lined processing equipment may also be used incertain applications.

A process flow diagram in accordance with one or more embodiments of themethods and systems described here is shown in FIG. 3. The processequipment and chemical reactions are similar to those shown in FIG. 2,with the exception that the source of oxygen fed to reactor 303 is pureoxygen.

The process system 30 includes contactor 301, where H₂S feed stream 300may be introduced and mixed iodine, which may be in the form ofiodine-rich solution, 306. Contactor 301 may be pre-heated by steam 326,to a temperature suitable for reaction conditions. H₂S reacts with theI₂ to produce stream 304, which exits contactor 301 and may comprise atleast one of elemental sulfur, iodide in the form of HI, un-reacted I₂,and other iodide salts. Off-gas 322 from contactor 301 may comprise atleast one of un-reacted CO₂, species, and small concentrations ofimpurities from the original H₂S feed stream. The off-gas may beadditionally treated to regenerate at least one of I₂ and CO₂.

Stream 304 may be introduced into separation device or separator 302,where elemental sulfur 320 may be precipitated off. The remainingportion from contactor 301 may produce stream 312, which may comprise atleast one of HI and other iodide salts. Iodide stream 312 may betransferred through first energy recovery device 313 to produce iodidesolution 314, which may be transferred through second energy transferdevice 308 to produce iodide solution 315. A first portion of iodidestream 315 produces iodide solution 305, which may be introduced intoreactor 303. A second portion of iodide stream 315 produces stream 309,which may be introduced into scrubber 307. Scrubber 307 may be used toregenerate additional I₂, in the form of regenerated iodine stream 310,which may exit scrubber 307 and may be further used to comprise aportion of iodine feed stream 306. Water 330 recovered or produced bythe scrubber may exit through one or more scrubber outlets. Scrubber 307may produce off-gas 328, comprising at least one of nitrogen, unreactedoxygen, and non-condensable gases. Pure oxygen 324 may be introduced toreactor 303 to produce iodine stream 311. Regenerated iodine stream 310may combine with iodine stream 311 to produce regenerated iodine stream316. For safety considerations, reactor 303 may not be constructed fromtitanium, but rather a material suitable for these particular reactionconditions, for example, Alloy C-276. In addition, the operatingtemperature in reactor 303 may be reduced when pure oxygen is used asthe reactant for iodine regeneration. For example, contactor 301 mayoperate at about 120° C., and reactor 303 may operate at about 80° C. Inaddition, the concentration of circulated iodine solution may bereduced, and the flow rates may be increased, for example, by 70% ormore.

When pure oxygen is used as the source of oxygen in reactor 303, theremay be significantly less off-gas produced for subsequent treatment byscrubber 307. The off-gas may contain at least one of nitrogen,un-reacted O₂, water produced by the reaction, and un-reacted I₂.Scrubber 307 may be used to regenerate additional I₂, in the form ofregenerated iodine stream 310, which exits scrubber 307 and may be usedto comprise a portion of iodine feed streams 306 and 316. Energytransfer device 308 may be in fluid communication with iodide streams314 and 315, as well as iodine streams 306, 310, 311, and 316.

A process flow diagram in accordance with one or more embodiments of thesystems and methods described herein is illustrated in FIG. 4. Theprocess system 40 comprises a contactor 401 configured for acountercurrent flow pattern. The countercurrent flow pattern includesintroducing H₂S feed stream 400 into a bottom portion of contactor 401and introducing iodine, which may be in the form of iodine-richsolution, 406, into a top portion or side portion of contactor 401,therefore producing the countercurrent flow. In the alternative, stream406 may be introduced into the bottom portion of contactor 401, whileH₂S feed stream 400 may be fed into a top or side portion of contactor401. Stream 406 may be pre-heated to temperatures near the operatingtemperature of the contactor. In addition, H₂S feed stream 400 may bepre-heated before being introduced to contactor 401. If necessary, watermay also be introduced to at least one of the H₂S feed stream andcontactor 401. The resulting reaction may produce stream 404, which maycomprise at least one of sulfur and iodide, and off-gas 405.

Contactor 401 may comprise one or more baffles and may be constructedand arranged to allow separation of one or more fluid phases. Off-gas405 from contactor 401 may comprise water vapor that may further becondensed and introduced to a scrubber to aid in I₂ regeneration. Stream404 from the contactor may be further introduced to at least one of acooler and a separation device, where elemental sulfur may beprecipitated out. The remaining reactants may then be further processedby, for example, a wet oxidation reactor, or may be transferred to ascrubber.

A process flow diagram in accordance with one or more embodiments of thesystems and methods described here is illustrated in FIG. 5. The processsystem 50 comprises contactor 501 configured for a co-current flowpattern. The co-current flow pattern includes introducing both H₂S feedstream 500 and iodine, which may be in the form of iodine-rich solution,506, into a bottom portion of contactor 501. Both streams may be allowedto flow upward together in a co-current flow pattern. In thealternative, stream 506 and H₂S feed stream 500 may be introduced into atop portion or a side portion of contactor 501. Stream 506 may bepre-heated to temperatures near the operating temperature of thecontactor. In addition, H₂S feed stream 500 may be pre-heated beforebeing introduced to contactor 501.

Contactor 501 may comprise one or more baffles and may be constructedand arranged to allow separation of one or more fluid phases. Theresulting off-gas and liquid reactant stream 504 may be furtherintroduced to at least one of a cooler and a separation device. Forexample, the off-gas may be separated from the liquid reactant and theliquid reactant may be separated into sulfur and liquid iodide solution.The liquid iodide solution may be further processed by, for example, awet oxidation process, or may be transferred to a scrubber. The off-gasfrom stream 504 may be further transferred and processed, for example,by a scrubber.

A process flow diagram in accordance with one or more embodiments of thesystems and methods described here is illustrated in FIG. 6. The processsystem 60 includes a reactor 603 configured to perform a wet oxidationreaction. Feed stream 605 may comprise iodide in the form of HIsolution. Feed stream 605 may further comprise a source of oxygen, suchas air. Reactor 603 may be configured with one or more baffles and maybe constructed and arranged to allow separation of one or more fluidphases, for example, the separation of gas and liquid phases. The wetoxidation reaction may produce iodine stream 611 and off-gas 610. Iodinestream 611 may be further introduced to an energy recovery device, forexample, a heat exchanger. Iodine stream 611 may be further introducedto at least one of a cooler and a phase separator. The resulting gasesmay be further treated by a scrubber to regenerate additional I₂. Iodinestream 611 may be further introduced to a downstream process, forexample, to a contactor, to react with H₂S gas. Off-gas stream 610 maycomprise water vapor that may be further condensed and introduced, forexample, to a scrubber.

EXAMPLES

The systems and methods described herein will be further illustratedthrough the following examples, which are illustrative in nature and arenot intended to limit the scope of the disclosure.

Example 1 Iodide Conversion to Iodine

A test was performed to evaluate the conversion of iodide and organiciodine compounds into elemental iodine. Testing was performed in ashaking autoclave.

The test conditions and results are presented in Table 1 below.

Feed Reactant Reactant Temperature — 240 260 (° C.) Oxygen Source — AirAir Reaction Time — 60 60 (min) Analysis pH 0.16 1.34 1.34 Iodide Salts880 86 52 (mg/L) Iodine (mg/L) — 2110 2200 Organic Iodine 1880 — 30Compounds (CH₃I)

-   -   indicates no reportable results

The results indicated that conversion of iodide salts and organic iodinecompounds can be accomplished using a wet oxidation process as describedherein.

Example 2 Removal of Sulfur from Acid Gas

A test was performed to evaluate the removal of sulfur from a gascomprising H₂S. An iodine-rich solution was placed into an impinger orcontactor and a gas containing H₂S was bubbled through it. Yellow sulfursolids were observed in the solution after a short period of time. Thepresence of precipitated elemental sulfur therefore showed thefeasibility of eliminating the Claus process for removing H₂S from a gasstream and replacing the process by using the systems and methodsdescribed herein.

Although the examples show the use of iodine to react with H₂S toproduce sulfur, it is within the scope of the methods and systemsdescribed herein to use other suitable compounds that are capable offunctioning as oxidizers and being regenerated, for example, by a wetoxidation process. Non-limiting examples of other compounds that may besuitable to use, include, but are not limited to, chlorine, bromine,manganese, vanadium, and fluorine.

Example 3 Removal of Sulfur from Acid Gas

A treatment system in accordance with one or more embodiments of thesystems and methods described here was evaluated for performance. Abench scale acid gas treatment with iodine was conducted under a numberof different test conditions.

Testing was performed in a Parr stirred autoclave fitted with titaniuminternals and head. The body was constructed of glass and had a volumeof 600 mL. The autoclave was equipped with a variable speed mixer andconfigured with multiple ports on the top to aid in at least one ofinjecting feed gases and venting reaction gases. Feed liquid was testedon a batch basis and test gases were tested on a flow-through basis.

The procedure for testing was as follows: (1) Introduce starting liquidto the autoclave, (2) Close autoclave and attach heating mantel toautoclave exterior, (3) Connect feed gas sources, (4) Start mixer, (5)Start temperature and pressure controls, (6) Start heater, (7) Startfeed gas flows, (8) After testing time period has elapsed, stop the gasflows, (9) Cool and depressurize the system, and (10) Recover the testsolution and submit for analysis.

A titanium autoclave was modified to function as a separator. Nozzleconnections were fitted to the top and bottom of the autoclave. Feed wasintroduced from the side and any condensate that formed descended to thebottom. The remaining components exited the separator and flowed to acooler.

A caustic scrubber was constructed of PVC. Off-gas passed upward throughthe scrubber where it was scrubbed with a 10% wt. caustic solution(NaOH) to aid in capturing any un-reacted H₂S. The scrubber wasconstructed to accommodate one liter of 10% caustic solution andadditionally contained a plastic packing material to increase thesurface area of the gas/liquid interface.

Off-gas from the autoclave was cooled by a tube-in-pipe cooler, whichwas constructed with an outer jacket and a tube or pipe of smallerdiameter and constructed of titanium. Cooling water flowed in the outertube counter-current to the off-gas flow. The outlet off-gas temperaturewas monitored by a thermocouple and recorded by a laptop programmablelogic controller (PLC).

Rheotherm gas flow meters were used to monitor gas flow rates of the H₂Sfeed stream, the air and nitrogen feeds to the autoclave, and the purgenitrogen to the separator. The gas flow meters were connected to alaptop PLC system, where gas flow rates were recorded.

The H₂S feed stream flow rate was controlled by a remotely operatedneedle valve and a block valve. The air and nitrogen feed gas flow rateswere controlled by a needle valve. A Dresser Masoneilan® pressurecontrol valve was used to control pressure in the autoclave using aFisher® controller.

The H₂S feed stream composition was 66% H₂S and 34% CO₂. The mixer speedwas set at 1700 rpm. Listed below in Table 2 are the test conditiondescriptions and details.

TABLE 2 Acid Gas Treatment with Iodine Reactor Temp./ Feed gas ReactionGas/ Test Pressure flow rate Time Flow rate Condition Condition Details(° C./psi) (lb/h) Iodine Additive (min.) (lb/h) 1 Initial analysis to 21/127 0.035 298 mL of 20 g/L I₂ 60 N₂/0.410 determine if I₂ treatsacid gas 2 Repeat condition  18/125 0.038 300 mL of 20 g/L I₂* 15N₂/0.434 1, reduce reaction time 3 Repeat condition 2 18.5/130  0.035300 mL of 26.7 g/L 15 N₂/0.403 with 40 g/L I₂/I⁻ I₂, 17.3 g/L I⁻ (KI)*mixture 4 Repeat condition 2  20/135 0.035 300 mL of 66.7 g/L 15 N₂/0.45with 100 g/L I₂/I⁻ I₂, 44.3 g/L I⁻ (KI)* mixture 5 Repeat condition125/125 0.035 290 mL of 66.7 g/L 15 N₂/0.44 4, increase temp, I₂, 40 g/LI⁻ (NaI) to 125° C. 6 Repeat condition 125/131 0.036 300 mL of 66.7 g/L30 Air/0.45 5, add Air I₂, 40 g/L I⁻ (NaI)* 7 Repeat condition 125/1280.036 275 mL of 13.3 g/L 30 Air/0.45 6, with 100 g/L I₂, 8.0 g/L I⁻(NaI) I₂/I⁻ mixture 8 Repeat condition 105/125 0.034 300 mL of 13.3 g/L15 N₂/0.45 5, reduce I₂, 40.0 g/L I⁻ (NaI) temperature 9 Repeatcondition 125/135 0.034 435 mL of 66.7 g/L 22 N₂/0.44 5, with one minuteI₂, 40 g/L I⁻ (NaI) acid gas residence time 10 Repeat condition 125/1350.070 285 mL of 66.7 g/L 7 N₂/0.73 5, reduce reaction I₂, 40.0 g/L I⁻(NaI) time. 11 Repeat condition 150/132 0.036 275 mL of 66.7 g/L 15N₂/0.45 5, increase temp, I₂, 40.0 g/L I⁻ (NaI) to 150° C. 12 Repeatcondition 5 125/130 0.035 290 mL of 100 g/L 15 N₂/0.44 with 100 g/L KIO₃KIO₃, 20 g/L (iodate) NaHCO₃ 13 Repeat condition 150/130 0.034 275 mL of66.7 g/L 10 N₂/0.45 5, reduce reaction I₂, 40.0 g/L I⁻ (NaI) time*Calculated result; no measurements taken.

Initial test reactions were performed at room temperature (20° C.) usingiodine in water. The system was nitrogen blanketed so that iodine wasthe only reactant in the system. The initial test runs resulted in highquantities of sulfur in the scrubber, indicating low acid gasconversion. This may have been due to deficient levels of iodine beingavailable in the solution.

Additional test reactions were performed where iodine was added withiodide (as KI or NaI) to form the soluble I₃ ⁻ complex. When asufficient amount of iodine was added to stoichiometrically treat allacid gas added to the system, no sulfur was detected in the scrubber,indicating a high degree of acid gas conversion. The sulfur producedalso contained iodine.

Further testing was performed where the temperature of the reactionvessel was increased to 125° C. or greater. This temperature range isabove both the melting point of sulfur (115° C.) and iodine (114° C.).Under these conditions, no detectable sulfide or other sulfur compoundswere detected in the scrubber, indicating that >99% of the sulfur addedto the system was removed from the gas and converted to elementalsulfur. The sulfur produced was a solid consisting of fine yellowparticles that settled quickly and appeared to be of high quality. Thistesting showed the superiority of the methods and systems of the presentdisclosure over the Clause process.

In addition to the elemental sulfur, small amounts of sulfate (H₂SO₄)were formed, with concentrations ranging from 90-600 mg/L, depending onthe specific test condition. In general, an increase in temperature alsoresulted in an increase in the concentration of sulfate in the effluent.Of the soluble sulfur compounds, sulfate was found to be the majorcontributor, with other soluble sulfur compounds, such as sulfide, beingminor contributors. Due to its corrosive nature, reaction conditions maybe tailored, for example, by keeping temperatures in a certain range, orbelow a certain target temperature, in order to minimize the formationof H₂SO₄. In the alternative, if the formation of H₂SO₄ is desirable,then the reaction conditions may be altered, for example, by increasingthe temperature, to increase the formation of H₂SO₄. Listed below inTable 3 are the test results.

TABLE 3 Results from Acid Gas Treatment with Iodine Scrubber EffluentPercent Sulfur Test H₂S Added Total Sulfur Sulfide Removed fromCondition (mg) (mg) (mg) H₂S feed stream 1 9300 7510 7460 19.2% 2 24001760 1530 26.7% 3 2100 981 917 53.3% 4 1900 90 <30 95.3% 5 2000 <10 <3099.5% 6 4500 <10 <30 99.8% 7 4400 2950 2640 33.0% 8 2100 <10 <30 99.5% 93300 <5 <30 99.8% 10 1800 <5 <30 99.7% 11 1900 155 128 91.8% 12 2100 18468 91.2% 13 1300 5.2 <30 99.6%

The bench scale acid gas treatment tests indicated that utilizing iodine(as the I₃ ⁻ complex regenerated by the WAO process) was sufficient fortreating acid gas at a temperature of 125° C. and a pressure of 135 psi.These conditions yielded concentrations of sulfur in the scrubber thatwere less than 10 mg/L, indicating >99% conversion. In addition, thesulfur produced appeared to be of high quality. The conversion reactionalso produced a small concentration of sulfuric acid. These resultsindicate that a very high conversion can be achieved, furtherreinforcing the superiority of the methods and systems of the presentdisclosure over the Clause process.

Example 4 Regeneration of Iodine

A treatment system in accordance with one or more embodiments of thesystems and methods described here was evaluated for performance. Abench scale iodide regeneration treatment was conducted under a numberof different test conditions.

Testing was performed in the Parr stirred autoclave, as described inExample 3, as well as a shaking autoclave. Listed below in Table 4 arethe test condition descriptions and details.

TABLE 4 Iodide Regeneration using Wet Oxidation Process Reaction Temp./Reaction Test Pressure Gas/Flow Time Condition Condition Details (°C.)/(psi) rate (lb/h) (min.) Reactant 1 Initial analysis to determine125/135 Air/0.45 15 100 g/L I⁻ conditions required for (as KI)regeneration of I₂ 2 Repeat condition 1, increase 150/135 Air/0.45 15100 g/L I⁻ temp. to 150° C. (as KI) 3 Repeat condition 2, increase150/135 Air/0.45 60 100 g/L I⁻ reaction time (as KI) 4 Repeat condition1, use 125/135 Air/0.45 15 100 g/L I⁻ spent iodine solution from priortreatment with acid gas 5 Repeat condition 4, increase 150/135 Air/0.4515 100 g/L I⁻ temp. to 150° C. 6 Repeat condition 5, increase 150/195Air/0.45 15  89 g/L I⁻ pressure 7 Repeat condition 6, 150/200 Air/0.4515 96.8 g/L I⁻  determine iodine balance 8 Repeat condition 6, increase150/200 Air/0.45 15 155 g/L I⁻ I⁻ concentration

Iodine regeneration tests were performed both in the shaking autoclaveas well as the semi-batch stirred autoclave. From these tests, it wasfound that iodine could be regenerated with temperatures as low as 80°C. and 15 minute residence times. In general, the regeneration of I⁻ toI₂ was approximately 50% (the theoretical maximum for I₂ conversion is67%). At higher temperatures and pressures, the conversion was morecomplete. In addition, higher pressures had a more significant impact atlower temperatures than at higher temperatures. For example, it isprojected that at a reaction temperature of 80° C., pressures of 400 psior greater would likely be required.

The results of at least one test condition indicated that in order forsufficient regeneration to occur, the solution must contain at least 67%of the total I⁻ species, meaning NaI, KI, and HI as HI. The I⁻ would notregenerate in any sufficient quantity if it was present only as NaI orKI without the addition of the acid. In other embodiments, it may bepossible to utilize a solution containing species that may be convertedto at least about 67% HI with, for example, the addition of HI. Theadditional 33% of the I⁻ in solution can remain as at least one of HI,KI, and NaI, and will not affect the regeneration since only the I⁻ ₃complex is formed. Listed below in Table 5 are the test results.

TABLE 5 Results from Iodide Regeneration using Wet Oxidation ProcessReactor Reactor Reactor Effluent Reactor Effluent Effluent I₂ TestVolume Effluent I⁻ + I₂ (calculated) % I₂ Condition (mL) I⁻ (mg) (mg)(mg) Regenerated Comment 1 — — — — — No iodine regeneration occurred. 2— — — — — No iodine regeneration occurred. 3 — — — — — No iodineregeneration occurred. 4 285 18582 28757 10175 35 Regenerationsuccessful. 5 275 15070 26620 11550 43 The increase in temperatureincreased regeneration of iodine. 6 285 11913 25337 13424 53 Theincrease in pressure increased regeneration of iodine. 7 300 13830 2826014430 51 The regeneration of iodine at 150° C. and 200 psi isapproximately 50%. 8 285 21375 44745 23370 52 A higher concentration ofiodide did not substantially affect the regeneration of iodine. —indicates no reportable results

Example 5 Multiple Cycle Evaluation

A treatment system in accordance with one or more embodiments of thesystems and methods described here was evaluated for performance. Abench scale multiple cycle treatment was conducted under a number ofdifferent test conditions.

The equipment used was identical to the equipment used in Examples 3 and4, with the exception that a second cooler was placed and configured ina vertical orientation at a location directly above the autoclave. Thesecond cooler functioned to condense gaseous iodine and recycle it backinto the autoclave. Repeated cycles included reacting gas comprising H₂Swith iodine followed by iodine regeneration. The cycles were performedmultiple times in succession to confirm that system efficacy was intactwithout the formation of additional compounds. Testing was performedwith a maximum of five complete oxidation and regeneration cycles.Listed below in Table 6 are the test condition descriptions and details.

TABLE 6 Multiple Cycle Analysis Reaction Time Temp./ (min.) TestPressure (For oxidation Condition Condition Details (° C.)/(psi) Gas andregeneration) 1 Initial analysis to determine if 125/135 N₂/Air 15 anyspecific compounds increase in concentration; 3 cycles 2 Repeatcondition 1, increase 150/135 N₂/Air 15 temp. to 150° C.; 5 cycles 3Repeat condition 2, increase 150/200 N₂/Air 15 pressure to 200 psi; 6cycles (last cycle did not have regeneration)

The test results indicated that there was little or no decrease in thetreatment capacity of the iodine, indicating that recycle in afull-scale iodine recycle system is possible. However, the amount ofsulfate (as sulfuric acid) did increase through multiple steps, withhigher concentrations at higher temperatures. This indicated that asulfate removal process may be required in a full-scale system. Listedbelow in Table 7 are the test results:

TABLE 7 Multiple Cycle Analysis Test Results Test Test Test ConditionCondition Condition Source Analysis Results 1 2 3 Autoclave Total Sulfur(mg)  193* — 932 Effluent Sulfate (mg) 162 — 938 Suspended Solids  83 —— (mg) Iodide (mg) 18,126   — — Iodide + Iodine (mg) 25,732   — 19,280Calculated Iodine 7,606   — — (mg) Separator Iodide + Iodine 8,330   — —Condensate (mg/L) Scrubber Total Sulfur (mg) 840 — 840 Solution Sulfide(mg) 852 — 2222 Autoclave (mL) 265 110 200 Separator (mL)  35 180 100Scrubber (mL) 1000  — 1000 *Total sulfur added to system could not bedetermined — indicates no reportable results

Results from the testing indicated that iodine was present in theoff-gas tubing exiting the reaction vessel. This occurred during boththe oxidation and the regeneration process, and indicates that smallconcentration of iodine is volatile. A scrubber may therefore benecessary to regenerate the iodine.

Additional testing was performed with iodate as the oxidizer and theresults indicated that the use of iodate was not as effective as iodinein treating acid gas. In addition, sufficient regeneration of the iodatedid not occur with WAO regeneration temperatures as high as 300° C.

Results from additional testing also indicated that the presence ofadditional additives that are capable of raising the pH, for example,ammonia, mono-ethanol amine, or phosphate, were found to interfere withthe regeneration of iodine.

While exemplary embodiments of the disclosure have been disclosed manymodifications, additions, and deletions may be made therein withoutdeparting from the spirit and scope of the disclosure and itsequivalents, as set forth in the following claims.

Those skilled in the art would readily appreciate that the variousparameters and configurations described herein are meant to be exemplaryand that actual parameters and configurations will depend upon thespecific application for which the systems and methods directed towardhydrogen sulfide treatment of the present disclosure are used. Thoseskilled in the art will recognize, or be able to ascertain using no morethan routine experimentation, many equivalents to the specificembodiments described herein. For example, those skilled in the art mayrecognize that the apparatus, and components thereof, according to thepresent disclosure may further comprise a network of systems or be acomponent of a hydrogen sulfide treatment system. It is, therefore, tobe understood that the foregoing embodiments are presented by way ofexample only and that, within the scope of the appended claims andequivalents thereto, the disclosed hydrogen sulfide treatment systemsand methods may be practiced otherwise than as specifically described.The present apparatus and methods are directed to each individualfeature or method described herein. In addition, any combination of twoor more such features, apparatus or methods, if such features, apparatusor methods are not mutually inconsistent, is included within the scopeof the present disclosure.

Further, it is to be appreciated various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe disclosure. For example, an existing facility may be modified toutilize or incorporate any one or more aspects of the disclosure. Thus,in some cases, the apparatus and methods may involve connecting orconfiguring an existing facility to comprise a hydrogen sulfidetreatment process. Accordingly, the foregoing description and drawingsare by way of example only. Further, the depictions in the drawings donot limit the disclosures to the particularly illustratedrepresentations.

What is claimed is:
 1. A method for treating hydrogen sulfide gas,comprising: reacting hydrogen sulfide gas with iodine to produce astream comprising iodide and sulfur; removing sulfur from the stream toproduce a separated stream comprising iodide; and reacting the separatedstream comprising iodide with a source of oxygen under aqueousconditions and at a predetermined temperature and a predeterminedpressure to produce a stream comprising iodine.
 2. The method of claim1, further comprising recovering at least a portion of the iodine fromthe stream comprising iodine.
 3. The method of claim 2, furthercomprising introducing at least a portion of the regenerated iodine tothe hydrogen sulfide gas.
 4. The method of claim 1, further comprisingrecovering elemental sulfur from the stream comprising iodide andsulfur.
 5. The method of claim 1, wherein the source of oxygen is air.6. The method of claim 1, wherein the predetermined temperature is in arange of from about 75° C. to about 260° C.
 7. The method of claim 6,wherein the predetermined temperature is in a range of from about 120°C. to about 175° C.
 8. The method of claim 1, wherein the predeterminedpressure is in a range of from about 25 psi to about 2000 psi.
 9. Themethod of claim 8, wherein the predetermined pressure is in a range offrom about 100 psi to about 400 psi.
 10. The method of claim 1, furthercomprising reacting the separated stream comprising iodide with a sourceof oxygen under aqueous conditions for a time period in a range of fromabout 15 minutes to about 120 minutes.
 11. The method of claim 10,wherein the time period is less than about 15 minutes.
 12. The method ofclaim 1, further comprising recovering thermal energy from the streamcomprising iodine.
 13. A system for treating hydrogen sulfide gas,comprising: a contactor fluidly connected to a source of hydrogensulfide gas and a source of iodine; a separator fluidly connecteddownstream from the contactor and configured to separate elementalsulfur and iodide; and a reactor fluidly connected downstream from theseparator and the separated iodide and fluidly connected to a source ofoxygen.
 14. The system of claim 13, further comprising a control systemconfigured to regulate a predetermined temperature and predeterminedpressure of the reactor.
 15. The system of claim 13, further comprisingat least one scrubber fluidly connected downstream from the reactor andupstream from the source of iodine.
 16. The system of claim 13, furthercomprising at least one energy recovery device fluidly connecteddownstream from the reactor and upstream from the contactor andconfigured to recover thermal energy from the reactor.
 17. The system ofclaim 13, further comprising a reactor outlet fluidly connected upstreamfrom the contactor and configured to transfer at least a portion ofregenerated iodine from the reactor to the contactor.
 18. The system ofclaim 17, wherein the rate of regeneration from iodide to regeneratediodine from the reactor is at least 50%.
 19. The system of claim 13,further comprising a scrubber fluidly connected downstream from thereactor and configured to transfer at least a portion of regeneratediodine from the reactor to the contactor.